The invention relates to a device for moving sheaths of nuclear fuel elements of the type comprising a stack of fuel pellets in the sheath at a filling station where a plurality of operations are carried out in succession.
Apparatuses for filling nuclear fuel element sheaths are already known. An apparatus described in French Pat. No. 2,257,130 comprises a vibrating table which causes pellets to enter through one end of a sheath closed at the other end and along the sheath.
It is an object of the invention to provide a device which is adapted to receive a plurality of sheaths, to bring them automatically to locations where successive operations take place and to place the sheaths on a rack after they have been loaded with pellets, for removal and transport to an other station. It is a more specific object to provide a device which is adapted to reduce the overall time which is necessary to fill a predetermined number of sheaths by carrying out different operations on successive sheaths at the same time. It is a more specific object to provide an apparatus in which the filled sheaths are finally arranged as a layer which may be lifted by the same machine which was previously used to place the empty sheaths on a laying rack.
For that purpose, there is provided a device comprising a first station for storage of empty sheaths as a horizontal layer of a plurality of empty sheaths in spaced relation to each other with a predetermined mutual spacing; a second station for storage of filled sheaths as a horizontal layer of a plurality of filled sheaths; sheath-loading means located between said first and second stations on a transfer path of said sheaths along a predetermined direction; first conveyor means for simultaneously engaging said plurality of empty sheaths and moving them as a whole toward said loading means; first pitch change means associated with said first conveyor means for repeatedly bringing part of the plurality of sheaths to a loading location confronting said sheath-loading means with a spacing which is different from said predetermined mutual spacing, for simultaneous filling of the sheaths by means already known; second pitch change means for repeatedly removing said part of the plurality of sheaths from said loading location and bringing them back to said predetermined mutual spacing; second conveyor means associated with said second pitch change means for moving said plurality of sheaths from said second pitch change means to said second station; and control means for synchronized actuation of said means.
It will be appreciated that all movements of the sheaths take place in the same, typically horizontal, direction. The pitch changing means will typically comprise "pilgrim step" conveyors. The pitch changing means will be constructed and arranged for each operation to take place with an appropriate spacing between adjacent sheaths, while the first and second stations, which may consist of laying and pick up racks, respectively, may be dimensioned for the surface required for storing the layer to be the minimum compatible with engagement by lifting means. The pitch changing means may each comprise two units, one for enlarging the mutual spacing and authorizing such operations as weighing or cleaning, and one for narrowing that spacing.
The sheath-loading means will typically include a vibrating table associated with retractable indexing means for inserting the open end of the sheath to be loaded acurately in indexing noses and then for maintaining them during filling for a description of the way sheaths are typically filled by the vibrating table, reference may be made to French No. 2 257 130 already mentioned.
The invention will be better understood from the following description of a particular embodiment of the invention, given by way of example. The description refers to the accompanying drawings.